I used linux before (suse, but here you don't really need to configure anything)

So I decidec to install gentoo and learn some more.
But I have some problems with compiling my kernel.
I don't know which options to activate and which to disable.

What I need in the kernel is support for the following
Soundblaster Live
Networkcard (realtek 8139)
Harddrives (2 ide drives, I want to enable DMA)
CDRW (plextor on IDE Channel)
DVD (pioneer on IDE CHANNEL)
Power management (I don't know which of the options I have to activate, but I have a recent computer).

Power management (I don't know which of the options I have to activate, but I have a recent computer).

Well, you can't really do anything interesting with ACPI yet so I'd leave it disabled. Go to General Setup -->

And enable Power Management Support, Advanced Power Management, Enable PM at boot time & Make CPU Idle calls when idle.

I checked those because they were what was enabled on a stock RH kernel. Also because it prevents an unavailable APM warning in XFree and I'm a bit bothered about warnings, however irrelevant they are!

With the kernel, I wouldn't worry if you don't check off options that you need. You'll soon find out about them and it's easy to put them right.